Interfacing cultured neurons to microtransducers arrays: A review of the neuro-electronic junction models

Microtransducer arrays, both metal microelectrodes and silicon-based devices, are widely used as neural interfaces to measure, extracellularly, the electrophysiological activity of excitable cells. Starting from the pioneering works at the beginning of the 70's, improvements in manufacture methods, materials, and geometrical shape have been made. Nowadays, these devices are routinely used in different experimental conditions (both in vivo and in vitro), and for several applications ranging from basic research in neuroscience to more biomedical oriented applications. However, the use of these micro-devices deeply depends on the nature of the interface (coupling) between the cell membrane and the sensitive active surface of the microtransducer. Thus, many efforts have been oriented to improve coupling conditions. Particularly, in the latest years, two innovations related to the use of carbon nanotubes as interface material and to the development of micro-structures which can be engulfed by the cell membrane have been proposed. In this work, we review what can be simulated by using simple circuital models and what happens at the interface between the sensitive active surface of the microtransducer and the neuronal membrane of in vitro neurons. We finally focus our attention on these two novel technological solutions capable to improve the coupling between neuron and micro-nano transducer

Particles at Membranes and Interfaces

Soft surfaces experience morphological changes upon interaction with objects at various length scales. Two important classes of soft surfaces are membranes and interfaces. In presence of particles, through surface-mediated interactions soft surfaces exhibit diverse phenomena in nature. A fluid membrane which acts as a protective periphery enclosing cellular material can be described as a two dimensional mathematical surface characterized by `bending elasticity' and `membrane tension'. Similarly, interfaces at the boundary of two liquid phases or a liquid and a gas phase are characterized by their interface tension. Interestingly, a close interplay of the deformation energy of these soft surfaces and the geometry and form of the particles allows the particles to interact. Thus, the study of interactions of particles with membranes and interfaces forms the basis of this work. The mechanistic aspects of cellular entry via membrane wrapping for particles of various geometries are studied theoretically and numerically. Such systems are characterized by the membrane bending rigidity, the membrane tension, and the adhesion strength. The different wrapping states exhibited are ``non wrapped", ``partially wrapped" (with low and high wrapping fraction), and ``completely wrapped". There are two kinds of phase boundaries: a continuous binding transition and a discontinuous transition either between two partially-wrapped states or from a partially-wrapped to a completely wrapped state. The theoretical analysis predicts stable partially wrapped states for nonspherical particles. Nonspherical particles having flat sides can show preferential initial binding though the decisive factor for encapsulation is the ratio of the width to the length of the particles and the softness of its edges. Wrapping energy contributions of the erythrocyte membrane to the invasion energetics for a malarial merozoite that has an asymmetric ``egg-like'' shape is assessed. Furthermore cell adhesion to nanopatterned substrates is characterized to predict optimal shapes of 3D nanoelectrodes for efficient coupling to cells using deformation energy calculations. For a fluid interface dominated by an interfacial tension, self-assembly via capillary interactions for micron-sized nonspherical particles is reported. A nonspherical particle can induce interface distortion due to an undulating contact line creating excess interfacial area. Neighboring particles interact to minimize the excess area via long-range interface-mediated capillary forces. The particle-induced interface distortion due to single ellipsoidal or cuboidal particles are calculated. The near-field nature of the capillary interactions between a pair of particles in different relative orientations is characterized using power-law fits

Bioengineered microfluidic devices for the real-time clinical measurement of neurochemicals

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. The focus of my research project is the study of potassium dynamics in spreading depolarisation (SD) waves found in TBI. The SD waves occur following the injury and the ionic imbalance caused by these waves causes further brain damage and greater patient morbidity. The goal of my research is to detect these waves in real time and quantify their severity in order to help clinicians better understand and treat TBI quickly and effectively to improve patient outcomes. During my thesis project, I have first developed a miniaturised ion-selective electrode (ISE) for the detection of potassium (K+) transients associated with SDs. The average K+ ISE has a Nernstian sensitivity of 58.9 mV dec^−1 and temporal response of 5.1 seconds in the physiological range. The ISE, housed in a microfluidic flow cell with a sample volume of 70 nL, was applied in in vivo microdialysis studies to monitor real-time depolarisation waves. An SD wave causes the dialysate K+ to increase by 0.42 +/- 0.07 mM and 1.13 +/- 0.63 mM, from the physiological normal of 2.7 mM, in the animal model and in the human injured brains respectively. This dialysate SD marker has also been validated against tissue K+ level and cortical electrical activity which are currently the gold standards for SD detection. In continuous or single-phase laminar flow, Taylor dispersion prevails. The result is an attenuated measured concentration to that captured at the microdialysis probe. With the development of a droplet microfluidic system, the dialysis stream can be segmented into discrete droplets suspended in a carrier oil, preserving the original concentration character-istics of the sample as well as improving the temporal resolution by ten-fold. The sample droplets can be manipulated passively to fulfil a range of operations, such as fast mixing, merging and splitting, and to enable parallelisation of analysis. Lastly, the droplets, now the core unit of analysis, are also reliably detected using a newly developed miniaturised contactless device based on conductivity, removing the need of expensive optical equipment and interference with the chemistry of the droplet.Open Acces

Single Cell Analysis

Cells are the most fundamental building block of all living organisms. The investigation of any type of disease mechanism and its progression still remains challenging due to cellular heterogeneity characteristics and physiological state of cells in a given population. The bulk measurement of millions of cells together can provide some general information on cells, but it cannot evolve the cellular heterogeneity and molecular dynamics in a certain cell population. Compared to this bulk or the average measurement of a large number of cells together, single-cell analysis can provide detailed information on each cell, which could assist in developing an understanding of the specific biological context of cells, such as tumor progression or issues around stem cells. Single-cell omics can provide valuable information about functional mutation and a copy number of variations of cells. Information from single-cell investigations can help to produce a better understanding of intracellular interactions and environmental responses of cellular organelles, which can be beneficial for therapeutics development and diagnostics purposes. This Special Issue is inviting articles related to single-cell analysis and its advantages, limitations, and future prospects regarding health benefits

Equivalent Circuit of the Neuro-Electronic Junction for Signal Recordings From Planar and Engulfed Micro-Nano-Electrodes

In the latest years, several attempts to develop extracellular microtransducers to record electrophysiological activity of excitable cells have been done. In particular, many efforts have been oriented to increase the coupling conditions, and, thus, improving the quality of the recorded signal. Gold mushroom-shaped microelectrodes (GM\u3bcE) are an example of nano-devices to achieve those requirements. In this study, we developed an equivalent electrical circuit of the neuron\u2013microelectrode system interface to simulate signal recordings from both planar and engulfed micro-nano-electrodes. To this purpose, models of the neuron, planar, gold planar microelectrode, and GM\u3bcE, neuro-electronic junction (microelectrode\u2013electrolyte interface, cleft effect, and protein-glycocalyx electric double layer) are presented. Then, neuronal electrical activity is simulated by Hspice software, and analyzed as a function of the most sensitive biophysical models parameters, such as the neuron\u2013microelectrode cleft width, spreading and seal resistances, ion-channel densities, double-layer properties, and microelectrode geometries. Results are referenced to the experimentally recorded electrophysiological neuronal signals reported in the literature

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand